The present invention relates to vehicle suspension for driven axles of amphibious vehicles.
In an amphibious vehicle, it is desirable to reduce drag when in marine mode, particularly drag caused by disconformities in those parts of the vehicle in contact with the water. Some such vehicles have retracting wheels with recesses above the water-line for the wheels to retract into. In the case of a planing amphibious vehicle, the hull recesses are generally above the water-line when the vehicle is on the plane; or in the case of our co-pending application no. WO 04/103743A1, plates are fitted to the vehicle's bottom to cover as much as possible of the recesses for the rear driven wheels. Such plates are fixed after assembly of the vehicle suspension during manufacture. Nevertheless, tramping caused by hitting waves or wakes; or alternatively cornering; can cause the wheel recesses to catch the water, which may in turn slow or slew the vehicle. To minimize such effects, it is essential to minimize the length of such recesses in the longitudinal direction of the vehicle.
The use of upper and lower wishbone suspension has the advantage of bracing the suspension against torque input and vibration. It is also convenient to locate spring and damper units within the wheel retraction recesses; but as can be seen from WO 04/103743A1, both of these measures lead to large recesses in the vehicle hull.
Where an amphibious vehicle is based on passenger car conventions of vehicle packaging, seating across the vehicle will be provided, and wheel arches will be blended into the vehicle bodywork. However, if alternative packaging concepts from lighter and more compact vehicles are considered, different opportunities and challenges arise. Where seating is arranged longitudinally along the vehicle, it can be made narrower than a passenger car. Particularly where the power train is also aligned along the vehicle, a greater hull vee angle can be considered than for a passenger car type body with transverse seating and engine. The large vee angle offers agile marine handling, but requires the use of large diameter road wheels to give adequate ground clearance; which would suggest large wheel arches and bulky suspension.
Should these large wheel arches be integrated into the vehicle body styling, they would tend to negate the compactness and light weight of a narrow amphibious vehicle. This is emphasised with a large hull vee angle, as the wheels must be retracted through large angles to stay above the water-line when the vehicle is canted on water. However, if the wheel arches are allowed to protrude beyond the contours of the rest of the vehicle bodywork, the main structure of the vehicle can still be narrow and light in weight. Hence, a new incentive is found to provide a compact yet sturdy amphibious vehicle retractable suspension which requires minimal hull recesses. Similarly, if seating is provided substantially above the vehicle power train, rather than in front of the power train or behind it, the hull will be relatively short; so it becomes critically important to minimize interruptions to the planing surface.